Method and apparatus for starting the boiler of a solid-fuel fired power plant and ensuring the burning process of the fuel

ABSTRACT

A method and apparatus starts the boiler of a solid-fuel fired power plant and ensures the burning process of the fuel. The main fuel of the boiler is ignited by entering an auxiliary fuel stream gasified and ignited with a plasma torch (1). Efficient mixing and safe ignition of the main fuel with the auxiliary fuel is ensured by a turbulent feed of the auxiliary fuel and a nozzle (12) through which the auxiliary fuel is entered into the main fuel stream.

BACKGROUND OF THE INVENTION

The present invention relates to a method for starting the boiler of asolid-fuel fired power plant and for ensuring the burning process of thefuel.

The invention also concerns an apparatus used for the implementation ofthe method.

DESCRIPTION OF THE BACKGROUND ART

Solid-fuel fired boilers of power plants are provided with severalburners. The primary proportion of the boiler energy output is producedby main burners which deliver the major quantity of fuel used for firingthe boiler. In boilers fired with a low-grade solid fuel, the continuouscombustion of the fuel must be ensured, since extinction of the firecauses an explosion hazard through the gasification of the fuel in thehot boiler into a gas containing explosion-susceptible carbon monoxide.The continuous combustion of fuel is ensured by means of auxiliarytorches. The auxiliary torches typically are different kinds of oil orgas torches.

A boiler fired with a solid fuel such as coal or peat is started (alsocalled "warm-up") by heating the boiler to a sufficient heat by theigniting torches, after which the feed of the solid fuel into the boilercan be initiated. The capacity of the igniting torches necessary in theprocess must be relatively high in relation to the total capacity of theboiler in order to make the starting operation possible. As a rule, theigniting torches are dimensioned so that their capacity is approx. 25 .. . 50% of the total capacity of the boiler.

The igniting burners conventionally used are gas or oil torches, whichsimultaneously function as combustion supporting torches. The mainburner in the boiler is mounted to an opening in the boiler wall, whilethe igniting auxiliary torch is placed in the center of the main burner.During the warm-up phase the boiler is heated by the auxiliary torchflame. When required, the igniting torch is used in the steady-stateoperation of the boiler as an auxiliary burner in the purpose ofensuring the continuous combustion of the main fuel. The function andconstruction of different kinds of gas and oil torches is well known inthe art.

The use of plasma torches as auxiliary and/or igniting burners has beeninvestigated, yet wider use of these apparatuses is still unseen.Further, the direct use of arc-ignited pulverized coal for the ignitionand auxiliary firing of the boiler is also being investigated, butequipment based on this idea is neither yet applicable at the scale ofpower plants. The state of the art is elucidated in the followingpublications

[1] Plasma torches as replacement for oil burners, S. L. Thunberg, W. J.Melilli, W. H. Reed, Energy, Iron and Steel International, December1983, pp. 207 . . . 211.

[2] Plasma torch boiler ignition, M. B. Paley, Babcock and WilcoxCanada, Industrial opportunities for plasma technology, Symposium inToronto, Oct. 21, 1982, D-2, 15 pp.

[3] Get oil and gas out of pulverized-coal firing, John Reason, Fuelsand fuel handling, Power, May 1983, pp. 111 . . . 113.

In addition to the above described implementations, an auxiliary burnerbased on multistage firing is known in the art in which the coal actingas the auxiliary fuel is delivered into the flame of a gas torch. Thefuel mix delivered into the torch flame is air-deficient, whereby theauxiliary air required for complete combustion is fed into the stream ofthe auxiliary fuel through a separate adapter. Conventionally usedignitor and auxiliary burner constructions based on oil or gas torcheshave a simple structure and achieve a well-behaved control of thecombustion process by means of these burners. The disadvantage of thesesystems is, however, that the torch uses a different fuel from that usedfor firing the boiler, whereby a separate fuel feed and storage systemmust be constructed for the torch. Oil and gas are priced aboveconventionally used solid fuels, and since the capacity of ignitors andauxiliary burners must be relatively high in relation to the totalcapacity of the boiler, they consume the high-priced fuels in abundance,thereby raising the operating costs of the plant. The combustion oflarge quantities of oil in conjunction with the use of a solid fuelappreciably increases the sulfur release rate of the plant, since theoil grades conventionally used contain substantially more sulfur thanthe conventionally used solid fuels. In peat-fuelled power plants inparticular, the contribution of oil-related sulfur is high in the totalsulfur releases of the plant, because the oil torch must be usedcontinuously in the steady-state operation of the boiler, thusnullifying the low sulfur content of peat. The combustion process ofpeat is difficult to control due to large variations in the moisturecontent and other combustion-related properties of peat. The majorproportion of sulfur releases from a peat-fired boiler is thus traceableto the oil used in the auxiliary burner.

Auxiliary burners and ignitors based on plasma technology are hamperedby their deficient capacity and small size of the plasma torch flame,therein making the combustion process of the main fuel difficult tocontrol by means of these apparatuses. The cold-start characteristics ofplasma-ignited burners are poor. Burners known in the art have beenunsuccessful in achieving a sufficient efficiency in the blending of theplasma flame with the fuel as to ensure a safe ignition of the fuel incold-start conditions. These apparatuses are incapable of safelystarting a cold boiler, making it impossible to use them as areplacement to a conventional igniting torch. Firing with low-gradefuels necessitates the use of an oil or gas supplementary burner tocomplement a plasma-ignited auxiliary burner.

An arc-ignited burner is applicable only as the main burner of a boiler.According to this method, electrodes are introduced into the fuel streamof the main burner, an arc is initiated between the electrodes, andafter the ignition of the fuel, the arc is extinguished and theelectrode structure is withdrawn from the fuel stream.

A disadvantage of a multistage gas-ignited burner is that the gas torchis incapable of generating a sufficiently hot and concentrated flame,which could achieve an efficient gasification of the auxiliary fuelmixture in sufficiently air-deficient conditions. The combustion airrequired by the gas torch further promotes combustion of the auxiliaryfuel already in the first stage of air feed. Consequently, thegas-ignited burner fails to achieve a sufficiently efficient multistageburner. In spite of the multistage combustion, the sulfur emissions fromthis kind of a burner are relatively high and the burner is unstable inoperation. In addition, this type of burner cannot achieve an efficientinitial operation of multistaged combustion at burner ignition.

Nitrogen oxide emissions from other types of burners described above areslightly higher than those of a gas-ignited multistage burner.

SUMMARY OF THE INVENTION

The aim of this invention is to achieve a plasma technology basedauxiliary and igniting burner construction, capable of being used as areplacement for conventionally used oil and gas burners with significantconcurrent reduction in nitrogen oxide emissions.

The auxiliary and igniting burner in accordance with the invention islater called the PC (plasma-coal) burner in short.

The invention is based on gasifying and igniting a portion of theauxiliary fuel by means of a plasma torch and then delivering thisauxiliary fuel coaxially to the center of the main fuel stream, wherebya low energy output of the plasma torch is sufficient for thegasification and controlled ignition of a large quantity of deliveredauxiliary fuel. According to the invention, it is feasible to achieve anauxiliary and igniting burner with such a high capacity and easycontrollability that boiler warm-up with this burner is possible.

More specifically, the method in accordance with the invention ischaracterized by routing auxiliary fuel into an air-deficientgasification zone in the flame of a plasma torch burning in front of thetorch. The auxiliary fuel is gasified and partially combusted, thereinallowing the combustion energy of the auxiliary fuel to gasify moreauxiliary fuel. The degree of gasification of the auxiliary fuel iscontrolled by feeding air into the auxiliary fuel at least in one stage.The gasified, partially burning and air-deficient mixture of auxiliaryfuel is ignited by feeding air into the mixture. Then, the auxiliaryfuel stream is entered into the main fuel stream in order to ignite themain fuel.

Furthermore, the apparatus in accordance with the invention ischaracterized by a body tube extending essentially coaxially with thecenter axis of the main burner, for feeding the auxiliary fuel into themain fuel stream. A nozzle is positioned on the boiler-side end of thebody tube for feeding the auxiliary fuel stream into the main fuelstream. A space is adapted between the plasma torch and the coaxiallyaligned body tube, for feeding the auxiliary fuel into the plasma flameburning in the space between the plasma torch and the body tube. Atleast one air feed adapter for feeding air into the auxiliary fuelstream is provided to control its degree of gasification. An air feedadapter feeds secondary air into the air-deficient auxiliary fuel streamin order to achieve its final ignition.

The invention provides outstanding benefits.

The apparatus in accordance with the invention permits the replacementof oil and gas burners earlier used as auxiliary burners and ignitors.Because the PC burner uses a solid fuel, the provision of storage andfeed equipment for oil or gas can be avoided. The operating costs of thepower plant are reduced by the use of a low-price fuel in the auxiliaryburner and the management of fuel storage becomes easier by virtue ofthe reduced number of stored fuels. The proportion of electrical energyrequired by the plasma torch is small in relation to the total capacityof the PC burner. Reduced sulfur oxide emissions particularly inpeat-fuelled power plants are experienced when an oil burner is replacedby a plasma-ignited solid-fuel burning PC burner. Since the apparatus inaccordance with the invention is a multistage burner, the emissions ofnitrogen oxides can be maintained by the methods of multistagecombustion at a low level equal or even better than that achievable withconventional auxiliary burners. With the use of the plasma torch forgasification and ignition of the auxiliary fuel, sufficient energy canbe introduced to the gasification zone of the burner for the achievementof effective gasification in the burner and thereby improved multistagecombustion over conventional burners. Through the use of this kind of aburner, the nitrogen oxide emissions can even be reduced by using such agas, preferably nitrogen, as the plasma-forming gas that later formssingle-atom radicals in the plasma flame. Hence, a significant reductionof nitrogen oxide emissions is the dominant benefit of the presentinvention.

The flame of the PC burner is easily controllable and steady burningeven at low energy output levels. By virtue of its stable burningcharacteristic, the energy output level of the PC burner is easilycontrolled by adjusting the fuel feed rate. Therefore, the PC burner issuitable for use as an igniting burner in all solid-fuel fired boilersas well as the boiler output regulating burner. The PC burner inaccordance with the present invention achieves main fuel use in coal- orpeat-fuelled boilers over a vastly wider range of boiler capacity and atlower operating levels of energy output than is possible with theconventional technology. With the safe and economical control of theplant energy output, the plant can be used for peak-clipping in thedistribution network by way of being fired by the main fuel alone. Theconstruction of the PC burner in accordance with the invention is suchthat the continuous burning of the fuel used in the burner is ensured bymeans of a plasma torch, whereby the boiler can use difficult-to-burnfuels such as wood chips, lignin, etc. as the main fuel. Due to theextremely reliable operation and easy controllability of the PC burner,the main burners can be supported by the PC burners without thesupplementary use of oil or gas torches, since the risk of fireextinction and subsequent explosion hazard is extremely small.

The present burner can be installed in new boilers or it can be used forreplacing the ignitors and auxiliary burners of an existing boiler. Nomajor changes are required in the boiler construction, because thepresent boiler can be built so small in size that it can be mounted inconjunction with the existing main burner as a replacement for thedismantled auxiliary burner and its ancillaries.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, argiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is next examined in detail with the help of attacheddrawings which are given by way of illustration only, and thus are notlimitative of the present invention.

FIG. 1 shows diagrammatically the basic components of an apparatus inaccordance with the invention.

FIG. 2 shows diagrammatically an apparatus in accordance with theinvention installed in conjunction with a main burner.

FIG. 3 shows a detailed sectional drawing of an embodiment of thepresent apparatus installed in conjunction with a main burner.

FIG. 4 shows an alternative embodiment of the present invention.

FIG. 5 shows a further alternative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, a plasma torch 1 is used forgasification of a solid fuel, for instance, dense-phase pulverized coal.The degree of combustion-gasification ratio of the coal and air mixtureis controlled by means of multistaged air feed. The partially gasifiedand burning air-deficit mixture containing hot coal particles, carbonmonoxide and hydrogen is fed into the fuel stream of a main burner 6,whereby the main fuel is ignited. Air is fed to the ignition zone inorder to improve the combustion process.

FIG. 1 illustrates the operating principle of the present invention. Theplasma torch 1 is adapted to the conical rear part of a burner 5. Theburner 5 is fed with air-entrained dense-phase pulverized coal enteringvia an adapter 2. The dense-phase pulverized coal is conveyed around theplasma torch 1 to the front of the torch 1, where the hot plasma flamegasifies a part of the pulverized coal into carbon monoxidesimultaneously igniting the combustion of pulverized coal and carbonmonoxide. The burning carbon monoxide further gasifies more coalparticles and thus augments the effect of the plasma flame. Temperaturein this gasification zone is locally above 3500° C., preferably above4000° C., sufficiently high to dissociate a portion of the nitrogen gasused as the plasma-forming gas into radicals. The air volume required inthis stage as carrier for the fuel is so small that the coal-air mixtureentering the gasification zone in front of the plasma torch 1 isextremely air-deficient. Secondary air is introduced to the fuel streamvia an adapter 3 in order to control the degree of fuel gasification.Air is mixed with the fuel only sufficiently to allow a portion of thecoal to be gasified into carbon monoxide. The burning gas containingcarbon monoxide, hydrogen and hot coal particles in abundance is blownalong a tube into the fuel stream of the main burner. Gasification ofthe fuel can be further controlled by adding tertiary air in the fuelstream through an adapter 4.

The combination of the plasma torch 1 and the multistage combustiontechnology results in a burner, whose nitrogen oxide emissions areextremely low. In conventional burners, nitrogen oxides are generated inthose zones of the flame that have a high temperature. The PC burneravoids the formation of nitrogen oxides, since the plasma is generatedwithout combustion air or fuel. Consequently, the plasma zone operateswithout oxygen necessary for the formation of nitrogen oxides. The flameof the plasma torch 1 is extremely hot, thereby being capable oftransferring a large quantity of energy into the auxiliary fuel mixture.

Heat generation in the gasification zone is further improved by thepartial combustion of the auxiliary fuel. When nitrogen is used as theplasma-forming gas, it dissociates in the gasification zone from adiatomic gas into single-atom radicals. These radicals then react withthe nitrogen oxides, whereby diatomic nitrogen and oxygen gases areformed. The later combustion stages subsequent to the plasma torch havesuch conditions as to allow the formed single-atom radicals and nitrogenoxides to react with each other. The resulting combustion flue gasescontain extremely small quantities of nitrogen oxides, whereby nitrogenoxide emissions from the burner remain very low.

Illustrated in FIG. 2 is an example of the adaptation of the apparatusin conjunction with a main burner 6. The PC burner 5 is aligned parallelwith the center axis of the main burner 6 so that the PC burner 5 iscoaxially constructed to the center axis of the main burner 6. Fuel isintroduced to the PC burner 5 via an adapter 2 and the fuel is ignitedby the plasma torch 1. The fuel of the main burner 6 enters via anadapter 8 and the combustion air required by the main burner 6 is routedto the burner 6 via an air duct adapter 7.

Illustrated in FIG. 3 is an embodiment of the present invention. Inaddition to the PC burner 5 and the main burner 6, the apparatuscomprises fuel and air adapters 2, 7, 8, 9, the plasma torch 1, airconduction slots 10, 11 and a nozzle 12 of the auxiliary burner. Themain burner 6 is mounted on the wall of the boiler. The PC burner 5 isconstructed to the center axis of the main burner 6 and the end of thenozzle 12 protrudes further into the boiler than the orifice of the mainburner 6. The nozzle 12 of the PC burner 5 is attached to theboiler-side end of a body tube 13. The body tube 13 of the PC burner 5enters the main burner space through the wall of the main burner 6within a protective sheath 16. The entrance-side end of the protectivesheath 16 and the body tube 13 is provided with a combustion-air feedadapter 9. The feed adapter 9 carries the attached plasma torch 1 andfuel feed adapters 2 of the PC burner 5.

The plasma torch 1 is DC excited using nitrogen as the plasma-forminggas. The plasma torch is water-cooled. Dense-phase pulverized coal usedas the fuel is delivered to the front of the plasma torch 1 via theadapter 2. The fuel is fed air-entrained by means of a blower. The endof the fuel feed adapter 2 joining to the auxiliary burner 5 is roundedinto a jacket enveloping approximately a half turn around the body.Because of the rounded shape of the end of the adapter 2, the pulverizedcoal entering the PC burner 5 is made to swirl about the center axis ofthe PC burner 5. The developing turbulence promotes the mixing of thepulverized coal with air and the gasification of the coal in the firstair feed stage. The turbulent flame and convection of the gas flowpromote the mixing of the main fuel with the gas stream entering fromthe PC burner and thereby achieve the ignition and steady combustion ofthe main fuel stream.

Adapted in front of the plasma torch 1 are air conduction slots 10 and11. By varying the quantity of air flowing through the air conductionslots 10 and 11, the degree of fuel gasification can be varied in thedifferent stages. The first air conduction slot 10 is formed between afeed tube 14 and a nozzle cone 15. The nozzle cone 15 in front of theplasma torch 1 forms a space in which the pulverized coal is ignited andpartially gasified into carbon monoxide by the effect of the plasmatorch. The plasma torch can be operated in a sustained or intermittentmode in the burner. The air quantity required as carrier for pulverizedcoal delivery is so small that a low content of carbon monoxide isformed in this stage. From the nozzle cone 15 the coal-air mixture isejected into the feed tube 14. At the end of the nozzle cone 15,secondary air is introduced via the air conduction slot 10, whereby morecarbon monoxide is formed. The formed mixture is then conducted alongthe feed tube 14 to the nozzle 12. The entrance of the nozzle 12 at thejoint with the discharge end of the feed tube 14 is fed with airdirected along the second air conduction slot 11. With the help of thissecondary air, the combustion of the mixture discharging from the feedtube 14 is accelerated The partially burning gas containing carbonmonoxide, hydrogen and hot coal particles in abundance is ejectedthrough the nozzle 12 into the fuel stream of the main burner 6. Thepurpose of the nozzle 12 is to achieve a flame whose blending with themain fuel stream takes place at maximum efficiency. The blending of themain fuel with the flame of the auxiliary burner 5 is promoted by theswirl motion of the gas stream discharging from the auxiliary burner 5about the center axis of the burner.

The auxiliary burner has a multistage structure, in which the requiredcombustion air is introduced in several stages. A feed adapter 9 of thecombustion air is mounted to the entrance end of the body tube 13 in theauxiliary burner 5. The air feed adapter 9 is a jacket enveloping aconical end 17 of the feed tube 14 and the nozzle cone 15. The air feedadapter 9 thus forms a cavity, which contains the entrance ends of theair conduction slots 10 and 11. The first slot 10 discharging at thefront of the nozzle cone 15 starts from between the conical end 17 ofthe feed tube 14 and the nozzle cone 15. The second slot 11 dischargingat the entrance end of the nozzle 12 is formed between the feed tube 14and the body tube 13. The body tube 13 is lined with a protective sheath16. The purpose of multistage combustion is to reduce the nitrogen oxideemissions from the combustion process. The formation of nitrogen oxidesis reduced by maintaining reducing conditions at the stage of flameignition where high temperatures are encountered. The combustiontemperatures in the final combustion of the main fuel stream can be keptlow by means of the multistage combustion technology, thereby achievinga low level of nitrogen oxide formation.

The energy output level of the PC burner 5 is controlled by regulatingthe feed rate of pulverized coal. The energy output of the plasma torch1 is maintained constant. Because the plasma torch is capable ofigniting the pulverized coal delivered into the PC burner even at lowfeed rates of fuel to the burner, the PC burner can be used over theentire range from maximum capacity down to zero energy output. Theefficient controllability of the burner facilitates its use as a energyoutput regulating burner in solid-fuel fired plants.

Other alternative embodiments are also feasible within the scope of theinvention. The shape of the nozzle 12 is thus varied in accordance withthe desired characteristics of the igniting flame. Different kinds ofnozzle constructions with defined characteristics are well known in theart, making the case-by-case dimensioning and adaptation of the nozzleeasy in compliance with the laws of flow mechanics. Three differentnozzle constructions are illustrated in FIGS. 3, 4 and 5. As evidentfrom the figures, the position of the end of the nozzle 12 within themain burner 6 can be varied. The positioning of the nozzle 12 isdependent on the size and construction of the main burner 6 and theboiler.

Embodiments illustrated in FIGS. 4 and 5 have a simpler constructionthan that illustrated in FIG. 3. In the latter embodiments the end ofthe plasma torch 1 has been placed closer to the nozzle 12, and air isintroduced into the auxiliary fuel only in two stages. The secondary airfor the combustion process serving for gasification of the auxiliaryfuel ignited by the plasma torch flame is taken along with the auxiliaryfuel stream through an adaptor 2. The main fuel flow with carrier gasenters from a main fuel adapter 8, while the combustion air for the mainfuel is taken through a combustion air adapter 7 of the main burner 6.

In the exemplifying embodiment, coal is used as the fuel of theauxiliary burner. By virtue of its low sulfur content and homogeneousquality, it is a preferred fuel for the auxiliary burner. Other possiblefuels are, for instance, pulverized peat and wood chips, yet any fuel isusable that can be delivered into the burner by appropriate means.

The fuel can be fed into the auxiliary burner either using a curvedadapter as described in the example, whereby the fuel is forced into aswirl motion about the center axis of the burner, or alternatively, in alinear motion parallel with the axis of the burner.

The plasma torch 1 can be powered with DC or AC, and the plasma-forminggas can be any suitable gas such as nitrogen, carbon dioxide, compressedair, etc., while the reduction of nitrogen oxides dictates a preferencefor the use of such a plasma-forming gas that in the later combustionstages forms single-atom radicals capable of dissociating the oxides ofnitrogen. This kind of a gas is nitrogen for instance. The plasma torch1 can be operated at a constant energy output, while a plasma torch 1with controllable power allows further improvement in the adjustment andcontrol possibilities of the PC burner. The energy output of the plasmatorch 1 is designed according to the output capacity of the burner. Theinput power to the torch 1 is typically in the range 50 . . . 500 kW.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A method for starting a solid-fuel fired boilerand ensuring the burning process of the fuel, in which method the mainfuel of the boiler is ignited and its burning is ensured by an auxiliaryfuel torch flame where the auxiliary fuel can be identical to that usedas the main fuel, comprising the steps of:routing auxiliary fuel into anair-deficient gasification zone in the flame of a plasma torch burningin front of the torch, the auxiliary fuel is gasified there andpartially combusted, therein allowing the combustion energy of theauxiliary fuel to gasify more auxiliary fuel; controlling the degree ofgasification of the auxiliary fuel by feeding air into the auxiliaryfuel at least in one step; igniting the gasified, partially burning andair-deficient mixture of auxiliary fuel by feeding air into the mixture;and entering the auxiliary fuel stream into the main fuel stream inorder to ignite the main fuel.
 2. The method in accordance with claim 1,wherein the plasma-forming gas is such a gas which can form radicals inthe plasma flame that are capable of removing nitrogen oxides developedin the subsequent stages of the combustion process.
 3. The method inaccordance with claim 2, wherein the plasma-forming gas used isnitrogen.
 4. The method in accordance with claim 1, wherein theauxiliary fuel is entered into the main fuel stream so as to make itproceed only in the direction of the center axis of the main fuelstream.
 5. The method in accordance with claim 1, wherein thetemperature of the gasification zone is locally above 3500° C.
 6. Themethod in accordance with claim 1, wherein the auxiliary fuel isdelivered via a duct in front of a plasma torch, where the auxiliaryfuel is ignited and partially gasified, and the partially gasifiedauxiliary fuel is further entered through a nozzle into the fuel streamof a main burner.
 7. The method in accordance with claim 1, wherein theauxiliary fuel is gasified and combusted in stages by entering air intothe hot auxiliary fuel mixture in at least two different stages.
 8. Themethod in accordance with claim 1, wherein the auxiliary fuel is enteredinto the main fuel stream so as to make it swirl about the center axisof the main fuel stream.
 9. The method in accordance with claim 5,wherein the temperature of the gasification zone is locally above 4000°C.
 10. An apparatus for starting a solid-fuel fired boiler and ensuringthe burning process of the fuel, comprising:a plasma torch and a mainburner; a body tube extending essentially coaxially with a center axisof the main burner, for feeding the auxiliary fuel into a main fuelstream; a nozzle adapted to the boiler-side end of the body tube forfeeding the auxiliary fuel stream into the main fuel stream; a spacebetween the plasma torch and the coaxially aligned body tube, forfeeding the auxiliary fuel into the plasma flame burning in the spacebetween the plasma torch and the body tube; at least one air feedadapter for feeding air into the auxiliary fuel stream in order tocontrol a degree of gasification thereof; an air feed adapter forfeeding secondary air into the air-deficient auxiliary fuel stream inorder to achieve final ignition thereof.
 11. The apparatus in accordancewith claim 10, further comprising a feed adapter of the auxiliary fuel,adapted to envelop partially or entirely the body of the auxiliaryburner.
 12. The apparatus in accordance with claim 10, furthercomprising a feed adapter of the auxiliary fuel, coaxially adapted tothe body of the auxiliary burner.
 13. The apparatus in accordance withclaim 10, wherein the body tube of the auxiliary burner is arranged toenter the space of the main burner through the wall of the main burnerwithin a protective sheath.
 14. The apparatus in accordance with claim10, further comprising a feed tube for feeding the gasified auxiliaryfuel into a nozzle.